2. 1 15.2 Electrical energy and voltage Role play Energy changes in a circuit Voltage Measuring voltage ? Voltage round a simple circuit Cells in series and parallel Check-point 2

3. 2 15.2 Electrical energy and voltage Role play

4. 3 15.2 Electrical energy and voltage Role play Moving in hula hoopElectric circuit Energy inputCell Energy outputLight bulbs Conducting loopHands holding hoopConducting wire What is/are driven to move? Electrons in wire Analogy between moving in a hula hoop and an electric circuit: A B and C Hula hoop

5. 4 15.2 Electrical energy and voltage + – 1Energy changes in a circuit Battery drives free electrons to go round the circuit, from –ve terminal to +ve terminal. electrons gain energy from battery... the energy gained changes to heat and light electrons return to battery and gain energy again

6. 5 15.2 Electrical energy and voltage 1Energy changes in a circuit Simulation driving free electrons to go round

7. 6 15.2 Electrical energy and voltage 1Energy changes in a circuit

8. 7 15.2 Electrical energy and voltage 1Energy changes in a circuit Simulation Input = 4 JC -1 Output = 3 JC -1 Output = 1 JC -1

9. 8 15.2 Electrical energy and voltage 2Voltage Unit: volts (V), V = J C –1 Voltage = V = i.e. battery gives 4 J to 1 C of charge... 4 V 3 V 3 J is changed to heat and light when 1 C passes...

10. 9 15.2 Electrical energy and voltage 2Voltage

11. 10 15.2 Electrical energy and voltage 3Measuring voltage Voltage across 2 points is measured by a voltmeter. leads to +ve pole of battery leads to –ve pole of battery + – V + – V + – V + –

12. 11 15.2 Electrical energy and voltage 3Measuring voltage Simulation

13. 12 15.2 Electrical energy and voltage 3Measuring voltage If the voltmeter is connected in the wrong way round, the pointer will deflect to the other direction.  This may damage the voltmeter Voltage across 2 points can also be measured by a voltage sensor connected to a data-logger.

14. 13 15.2 Electrical energy and voltage 4Voltage round a simple circuit Voltage across the battery V V V = sum of the voltages across components 1 V 1 V + 3 V = 4 V 3 V

15. 14 15.2 Electrical energy and voltage 5Cells in series and parallel This battery has cells connected in series. Each unit charge gains energy from each cell. total voltage = sum of the voltages of all cells Total voltage = 9 V

16. 15 15.2 Electrical energy and voltage 5Cells in series and parallel Cells connected in parallel... total voltage = voltage of 1 cell each unit charge passes through one cell only. The cells can last longer. 1.5 V 1.5 V

17. 16 15.2 Electrical energy and voltage 5Cells in series and parallel In a parallel arrangement, the currents add up. In a serial arrangement, the voltages add up.

18. 17 15.2 Electrical energy and voltage Check-point 2 1A light bulb is…A light bulb is… 2How much energy...How much energy... 3How many joules of…How many joules of… 4The following photo…The following photo…

19. 18 15.2 Electrical energy and voltage Check-point 2 – Q1 A light bulb is connected to a 3-V battery. If the battery has delivered 12 J of energy to the bulb, how much charge has passed through the bulb? A1 CB4 C C6 CD12 C

20. 19 15.2 Electrical energy and voltage Check-point 2 – Q2 How much energy is supplied to each coulomb of charge that flows through a 9-V battery? Voltage =  9 J is given to each coulomb of charge electrical energy charge

21. 20 15.2 Electrical energy and voltage Check-point 2 – Q3 How many joules of energy are stored in this kind of rechargeable AA battery? Energy stored = QV = 1800 mA h x 1.2 V = 6480 C x 1.2 V = 7776 J

22. 21 15.2 Electrical energy and voltage Check-point 2 – Q4 The following photo shows some circuit components. Draw lines to connect the components according to the circuit diagram.

23. 22 15.2 Electrical energy and voltage The End

24. 23 15.2 Electrical energy and voltage Example 2 Energy change An iPod player needs a voltage of 6 V to operate. Suppose that it draws a current of 0.35 A when switched on. How much electrical energy is changed to sound and heat (a) when each coulomb of charge passes through the player circuit ; A voltage of 6 V means that 6 J of electrical energy is changed into other forms of energy for each coulomb of charge.

25. 24 15.2 Electrical energy and voltage Example 2 Energy change Charges flowed through in 10 min = Q= Q = It = 0.35  600 = 210 C An iPod player needs a voltage of 6 V to operate. Suppose that it draws a current of 0.35 A when switched on. How much electrical energy is changed to sound and heat (b) when the player has been switched on for 10 min? Total energy change in 10 min = E= E = QV = 210  6 = 1260 J

26. 25 15.2 Electrical energy and voltage Return